I had this same conversation yesterday and arrived at the same conclusion. The old G-38 is just what you said,not too powerful. The plus side is that they are hard to wear out and fairly easy to hand start even though they are a mag ignition.
I have one in a Ikon Monocoupe and find it a perfect match for that airframe.

For the Brown Racer I would certainly entertain the idea of the Brison or like engine and let the old G-38 make happy sounds in something else.

As a side note on the Brown it it is a B squared kit watch the wing center section as it will sometimes fold up in high g turns unless it has been reinforced or the flying wires are active.